Lots of IMAGINATION and some circular reasoning... that's how fossils are dated!
"The rocks do date the fossils, but the fossils date the rocks more accurately. Stratigraphy cannot avoid this kind of reasoning if it insists on using only temporal concepts, because circularity is inherent in the derivation of time scales."- J. E. O'Rourke; Amer. Journal of Science, Vol. 276, p.51
"And this poses something of a problem: If we date the rocks by their fossils, how can we then turn around and talk about patterns of evolutionary change through time in the fossil record?"- Niles Eldredge, Columbia Univ.; Time Frames, 1985, p.52
"It cannot be denied that from a strictly philosophical standpoint, geologists are here arguing in a circle. The succession of organisms has been determined by the study of their remains imbedded in the rocks, and the relative ages of the rocks are determined by the remains of the organisms they contain."- R. H. Rastall, Lecturer in Economic Geology, Cambridge Univ.: Encyclopaedia Britannica, Vol.10
(Chic: William Benton, Publisher, 1956, p.168
"The charge that the construction of the geologic scale involves circularity has a certain amount of validity... Thus, the procedure is far from ideal and the geologic ranges are constantly being revised (usually extended) as new occurrences are found."- David M. Raup, Chic. Field Museum, Univ. of Chic.; Field Museum of Nat. Hist. Bulletin; Vol.54
, Mar. 1983, p.21
"The intelligent layman has long suspected circular reasoning in the use of rocks to date fossils and fossils to date rocks. The geologist has never bothered to think of a good reply, feeling the explanations are not worth the trouble as long as the work brings results."- J.E. O'Rourke, Amer. Journal of Science 1976, 276:51.